linux-kernel - Re: [PATCH 0/2] Send a SIGCHLD to the init's pid namespace parent when reboot

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Date:	Tue, 23 Aug 2011 16:29:15 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Greg Kurz <gkurz@...ibm.com>
Cc:	Bruno Prémont <bonbons@...ux-vserver.org>,
	containers@...ts.linux-foundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Send a SIGCHLD to the init's pid namespace parent
	when reboot

On 08/23, Greg Kurz wrote:
>
> On Tue, 2011-08-23 at 15:33 +0200, Oleg Nesterov wrote:
> > [...]
> > At least now I understand why did you mention si_code/CLD before. You
> > meant waitid(). I thought you were talking about the death-notifications
> > which can't report CLD_ you need.
> >
> > I strongly object. We shouldn't uglify wait_task_zombie() to solve the
> > very specific problem.
> >
> > And once again. sub_init->parent does wiat(&status) and sees
> > WIFSIGNALED() && WTERMSIG(status) == SIGHUP. This can only mean that
> > sys_reboot(LINUX_REBOOT_CMD_RESTART) was called. It _can not_ be really
> > killed by SIGHUP, it must be CMD_RESTART.
> >
> > Why this can't work? Why do you want the additional complications?
> >
>
> I don't see either what could go wrong with you approach.

Thanks ;)

Just in case... instead of WIFSIGNALED/WTERMSIG we can also report
the exit code in the upper bits. I mean,

	switch (reboot_cmd) {
	case LINUX_REBOOT_CMD_RESTART:
		code = 1 << 16;
		break;
	case LINUX_REBOOT_CMD_HALT:
		code = 2 << 16;
		break;
	}

this can't be confused with the normal exit(code), just the parent
should be careful, I am not sure this can't confuse WIFEXITED/WEXITSTATUS
user-space macroses.

wait(&status) takes "int *", we have a room for additional info, and
wait_task_zombie() simply copies exit_code.

Oleg.

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